Droplet actuators are used to conduct a wide variety of droplet operations. A droplet actuator typically includes two plates separated by a space. The plates include electrodes for conducting droplet operations. The space is typically filled with a filler fluid that is immiscible with the fluid that is to be manipulated on the droplet actuator. A droplet on the droplet actuator is separated from one or more of the electrodes by a dielectric layer. The droplet may be grounded. For a variety of reasons described more fully herein, it may be useful to measure the capacitance of the dielectric layer between the electrode(s) and the droplet.